Since liquid crystal itself does not emit light, it is necessary to use an additional light emitting unit to improve the brightness of a display screen in a liquid crystal display. Currently, one of the generally used techniques is a backlight module with a diffusion plate. The diffusion plate is an important component of a backlight module. Not only diffuse reflection effect on the light but also good uniformity and transmissivity are important for a diffusion plate.
In the conventional technology, in order to improve the brightness and uniformity of a diffusion plate, the diffusion plate generally comprises a transparent substrate and a resin layer containing organic particles and/or inorganic particles. As disclosed in the U.S. Pat. Nos. 6,602,596 and 5,831,774, resin particles are bonded onto a substrate with adhesive, forming a coarse surface in a three-dimension structure and thereby improving turbidity and diffusion characteristics of the resultant diffusion plate.
In addition, in the Chinese patent CN1834756, it has been proposed that organic particles or inorganic particles are added into a substrate and pores are generated around the particles by longitudinal and/or lateral stretching of the substrate, and thereby transmissivity and diffusion of the light passing therethrough are improved.
The pores formed as disclosed in CN1834756 may improve transmissivity. Due to presence of the pores, when light enters a substance with relatively low refractivity from another substance with relatively high refractivity, total reflection phenomenon is prone to occur at the interface and thereby the energy loss of the light is reduced. However, the size of the pores is influenced by the varied boundary tension between the resin layer and the substrate and also by the applied stretching force, and therefore it is difficult to obtain satisfied manufacturing consistency, which leads to insufficient uniformity of the light.
Although addition of organic or inorganic particles into a substrate of a diffusion plate may enhance diffusion of light, the light passing therethrough is subject to repeated refractions in the light path before reaching the light outgoing surface of the diffusion plate, so a portion of the energy of the light is lost during the refractions such that the transmissivity of the light becomes relatively low.